Once there were two alicorn sisters: one guarded the day, the other the night. Over time the younger grew bitter and resentful, transforming into the beastial Nightmare Moon! In order to defend her little ponies, the elder wielded the power of the Elements of Harmony to banish Nightmare Moon. But the Nightmare was also a bearer of Harmony and used her power to inflict the banishing upon her elder as well. And thus; the two sisters were sealed in the celestial bodies: one in the sun, and one in the moon.

With the throne of Equestria left empty the nobility acted to secure their power. The unicorns put their earth pony and pegasus counterparts to the sword and created the Empire of the Horn under the rule of Emperor Blueblood the First. The superiority of unicorns was made law and all other species and races made secondary, with the exception of one. Humans were reduced to mere slaves, disposable and worthless.

Now, under the rule of Emperor Blueblood the 15th, the Empire marches forward, conquering and subjugating the last remnants of resistance on Equis. Such an endeavor requires untold effort, thousands of slaves die daily, but the archmages of Canterlot have found a solution: another world, teeming with humans, ripe for subjugation.

And so the door was opened, opened to the red planet named war.